I have no problems with the concepts, maybe a precision on that point(..I was really aiming at getting the AOP principles across without getting too detailed on how Spring achieves this..) would have helped to clarify the diagrams, because the article states in another direction ..., we focus on just the AO facilities provided by Spring. and ...This article will show you how to use the following AOP concepts as they are implemented in the Spring framework....

Sure conceptually before() is executed before foo() is called, but in order to understand it one has to say on which objects.

I can't get warm with those UML sequence diagrams (or aren't they meant to be?), either they should really show only the concept of AOP unrelated to a specific technology (e.g. it shows AppContext.getBean(), this is specific here in Spring and doesn't directly relate to AOP) or they should show what really happens when you use AOP and Spring (e.g. adding the missing Proxy and all would be clear
MainApp->getBean("bl")->IBusinessLogic.foo()->Proxy.foo()->before()->BusinessLogic.foo()->afterReturning()).

Anyway, thanks again for the clarifications,
I am curious about the Part 2 of your series.